Glucans are generally described as polymers of glucose and are derived from yeast, bacteria, fungi and plants. Glucans containing a .beta.(1-3)-linked glucopyranose backbone have long been known to have biological activity, specifically they have been shown to activate the immune system.
Neutral .beta.(1-3) glucan polymers are limited in their utility in parenteral pharmaceutical applications, however, because they are not readily soluble in physiological media. DiLuzto, U.S. Pat. No. 4,739,046 and Williams et al., U.S. Pat. No. 4,761,402. The primary reason for the inherent insolubility of .beta.(1-3) glucans is their tendency to form tightly associated triple-helical fibrils which resist hydration. For this reason, attempts to develop soluble .beta.(1-3) glucans depend on chemical substitution with charged groups, such as phosphate (U.S. Pat. Nos. 4,739,046; 4,761,402), amine (U.S. Pat. No. 4,707,471) or other functional groups (e.g., sulphate) which change the native conformation of the glucan molecules and may affect their biological and pharmacokinetic properties.